Quick Answer
Up to 5 cups (1.2 liters) of green tea per day is considered safe for most healthy adults. Drinking more than 5 cups may cause side effects due to the caffeine content. Green tea contains less caffeine than coffee, but the caffeine can accumulate and cause jitters, insomnia, irritability and headaches if consumed excessively.
How Much Caffeine is in Green Tea?
Green tea contains approximately 25-45 mg of caffeine per 8 ounce (237 ml) cup. The actual caffeine content varies depending on factors like the tea variety, brewing time, and water temperature.
Here’s a comparison of the caffeine content of green tea vs other beverages (1,2):
| Beverage | Caffeine (mg) |
|---|---|
| Green tea (8 oz) | 25-45 |
| Black tea (8 oz) | 25-48 |
| Coffee (8 oz) | 63-126 |
| Espresso (1 oz) | 47-75 |
| Energy drinks (8 oz) | 70-200 |
As you can see, an 8 ounce cup of green tea generally contains less caffeine than coffee, but more than decaf coffee or soda.
Is Caffeine in Green Tea the Same as Coffee?
The caffeine in green tea functions a bit differently than caffeine from coffee. Green tea contains L-theanine, an amino acid that works synergistically with caffeine to promote alertness without causing the “jittery” side effects typically associated with coffee.
L-theanine increases alpha brain wave activity which induces relaxation. This combination of relaxation and alertness from the green tea caffeine-L-theanine combo helps explain why many experience no anxiety or nervousness from green tea, even at high amounts.
Recommended Upper Limit Per Day
Most studies agree that up to 5 cups (1.2 liters) of green tea per day seems to be safe and provide health benefits for most healthy adults (3, 4).
This gives you 240-450 mg of caffeine if you are brewing a potent cup of green tea. 5 cups also provides 250-350 mg of L-theanine.
Drinking more than 5 cups (in excess of 600 mg caffeine) may cause unintended side effects including:
– Jitters, anxiety or nervousness
– Rapid heartbeat
– Insomnia
– Upset stomach
– Muscle tremors
– Headache
– Irritability
However, the amount can vary based on your personal caffeine tolerance. Some people are more sensitive to the effects of caffeine than others.
Tips to Adjust Caffeine from Green Tea
Here are some tips if you seem sensitive to the caffeine in green tea:
– Start slow – Drink 1 cup per day and gradually work up to more as tolerated. This helps your body adjust.
– Mix in decaf – Alternate cups of regular green tea with decaf green tea.
– Watch the brew time – Shorter infusions around 1-3 minutes deliver less caffeine than longer brew times.
– Choose lower caffeine teas – Look for a Fukamushi Sencha green tea or Houjicha roasted tea which contain lower caffeine.
– Drink earlier in the day – Caffeine’s effects last 4-6 hours. Avoid caffeine after 2 pm if it affects your sleep.
– Stay hydrated – Drink a glass of water for each cup of tea to help dilute the caffeine.
Does Green Tea Contain Tannins?
Green tea definitely contains tannins, which are natural plant compounds that have a bitter taste and can decrease the absorption of certain nutrients like iron.
However, green tea contains far less tannins than black tea or wine. A typical cup of green tea only contains around 10 mg of tannins (5).
For comparison, a cup of black tea provides 15-20 mg of tannins while 1 glass of red wine provides about 3500 mg of tannins (6).
So green tea only provides a small amount of tannins that is considered safe by most health organizations. Even consuming 5 cups a day would only amount to around 50 mg of tannins.
However, to limit exposure to tannins in general, avoid drinking green tea with meals (especially iron-rich foods like red meat) and wait at least an hour after eating before having green tea.
Does Green Tea Contain Oxalates?
Green tea leaves do contain oxalate, about 327-457 mg per 100 grams of dry leaves according to one study (7).
Oxalates can bind to calcium and cause kidney stones in those prone to the condition. While black tea contains more oxalates than green tea, this is generally not a concern for healthy adults drinking normal amounts of green tea.
To reduce oxalates, avoid drinking green tea on an empty stomach. The tannins in green tea can increase the absorption of oxalates, so consuming green tea with food helps limit oxalate absorption. Those with a history of calcium oxalate kidney stones may want to limit green tea to 1-2 cups per day.
Does Green Tea Impact Iron Absorption?
Yes, compounds in green tea including polyphenols and tannins can bind to non-heme iron from plant sources and reduce absorption a small amount (8).
One study found that drinking a cup of green tea reduced absorption of iron from a meal by 18% (9). This effect is not generally a concern for those eating a balanced diet high in bioavailable iron.
However those at risk of deficiency or with low ferritin levels may want to avoid drinking green tea alongside iron-rich meals or iron supplements. Waiting 1-2 hours to consume green tea is recommended.
Adding lemon juice to green tea has been shown to counteract the inhibitory effects on iron absorption (10). Vitamin C boosts iron absorption, so adding lemon, which contains vitamin C, can help offset the impact when drinking green tea with meals.
Does Green Tea Cause Stomach Issues?
Green tea is often touted for its benefits for gut health and digestion. However, for some people, green tea on an empty stomach may cause minor stomach upset or nausea.
Having a small snack like crackers before drinking green tea can help avoid this issue. Those with peptic ulcers or acid reflux may also want to avoid drinking green tea in large amounts.
The tannins in green tea increase stomach acid production, so green tea may irritate the stomach lining for those sensitive to acids (11).
Start with 1 cup per day taken with food and discontinue use if nausea, cramping or stomach irritation occurs. Avoiding drinking green tea in the evenings may also help for those prone to reflux symptoms.
Does Green Tea Impact Sleep?
The caffeine content in green tea can interfere with getting a good night’s sleep for some people. Especially if consumed in the late afternoon or evening.
The average half-life of caffeine ranges from 4-6 hours, so it’s best to avoid caffeine after 2pm if you have trouble sleeping (12).
Those very sensitive to caffeine’s effects may need to cease consumption by noon or 1pm instead. Luckily, L-theanine in green tea helps counteract some of the stimulatory effects of caffeine for some individuals.
If green tea does make it difficult to fall asleep, try sticking to 1-2 cups early in the day, diluted with water and avoiding strong brews. Switching to decaf green tea is recommended in the evenings and limiting consumption to 8 hours before bedtime.
Green Tea & Medication Interactions
The caffeine in green tea can potentially interact with certain medications and increase side effects. Caffeine should be limited if you take medications including (13):
– Anxiety medications like Lorazepam or Diazepam
– Blood pressure medications
– Some antidepressants
– Bronchodilators like Theophylline
– Antibiotics like Ciprofloxacin or Norfloxacin
– Stimulants like Ritalin
– Thyroid medications like Levothyroxine
Too much caffeine can also decrease lithium concentrations in the blood for those taking lithium to treat bipolar disorder. Speak to your doctor about any interactions with green tea if taking regular medications or prescriptions.
Does Green Tea Cause Diarrhea or Constipation?
Green tea is often promoted as an herbal remedy for both constipation and diarrhea due to its natural tannins and ability to influence GI motility.
However, both diarrhea and constipation are potential side effects if you consume too much green tea in a day.
The caffeine in green tea functions as a stimulant laxative which induces bowel movements. Excess intake may loosen stools too much leading to diarrhea.
On the other hand, the tannins in green tea have an astringent effect on the digestive tract that could cause constipation when consumed in large amounts by binding stools and drying out the intestines (14).
1-3 cups of green tea per day is unlikely to cause diarrhea or constipation in most people. But the laxative effects become more likely above 5 cups per day.
Is Green Tea Safe During Pregnancy?
While green tea in small to moderate amounts is likely safe, many doctors recommend limiting caffeine from all sources including green tea during pregnancy.
Green tea contains caffeine, which crosses the placenta barrier and could potentially affect the pregnancy or increase the risk of miscarriage and low birth weight babies if more than 200mg daily is ingested (15).
The American College of Obstetricians and Gynecologists recommends limiting caffeine from all sources to less than 200mg per day during pregnancy as a precaution (16).
Rather than counting milligrams, pregnant women are advised to limit green tea to about 2 cups per day, avoiding strong brews. Additionally, consuming green tea alongside food can help reduce the absorption of caffeine.
Can Children Drink Green Tea?
Green tea is likely safe for children in small amounts, but moderation is key. The minimum suggested age to introduce green tea is around 2 years old once the gut microbiome is more developed.
The main concern with giving green tea to children is the caffeine content. As a stimulant, caffeine intake should be restricted for kids and adolescents. Below are general caffeine guidelines by age (17):
– Toddlers under age 3: Avoid caffeine
– Children age 4-6: No more than 45 mg per day
– Children age 7-9: No more than 62 mg per day
– Children age 10-12: No more than 85 mg per day
– Teens age 13 and up: No more than 100 mg per day
To stay within recommendations, provide no more than 1/4 cup of very weak brewed green tea to younger kids per day. Older children and teens can have 1/2 cup of weak green tea once or twice a day at most. Also avoid giving green tea in the afternoons or evenings for children.
Additionally, wait until after age 1 to introduce green tea since the tannins may inhibit iron absorption at younger ages. Always dilute the tea well and monitor children for any reactions.
Conclusion
Based on the caffeine content, up to 5 cups (1.2 liters) of green tea per day can be safely consumed as part of a healthy diet for most adults. This provides 240-450 mg of caffeine.
Higher intakes may cause side effects like jitteriness, rapid heartbeat, insomnia, irritability and headaches in those sensitive to stimulants. Start slow and adjust your intake based on your personal tolerance.
Additionally, limit or avoid caffeine from green tea for pregnant women, children and those taking medications that may interact with caffeine. Enjoy green tea in moderation by following the guidelines in this article.
